Emergence of Visible‐Light Water Oxidation Upon Hexaniobate‐Ligand Entrapment of Quantum‐Confined Copper‐Oxide Cores

Abstract

The formation of small 1 to 3 nm organic‐ligand free metal‐oxide nanocrystals (NCs) is essential to utilization of their attractive size‐dependent properties in electronic devices and catalysis. We now report that hexaniobate cluster‐anions, [Nb6O19]8−, can arrest the growth of metal‐oxide NCs and stabilize them as water‐soluble complexes. This is exemplified by formation of hexaniobate‐complexed 2.4‐nm monoclinic‐phase CuO NCs (1), whose ca. 350 Cu‐atom cores feature quantum‐confinement effects that impart an unprecedented ability to catalyze visible‐light water oxidation with no added photosensitizers or applied potentials, and at rates exceeding those of hematite NCs. The findings point to polyoxoniobate‐ligand entrapment as a potentially general method for harnessing the size‐dependent properties of very small semiconductor NCs as the cores of versatile, entirely‐inorganic complexes.

Post‐synthetic Metalation on the Ionic TiO2 Surface to Enhance Metal‐CO2 Interaction During Photochemical CO2 Reduction

“…The Raman bands for the Anatase TiO 2 nanocore were consistent at 170 cm −1 , 520 cm −1 and 648 cm −1 (Figure S11) [49] . Almost 56 cm −1 band shifting of [W=O] t and 16 cm −1 of [W−O‐W] b due to copper exchange is implicating a possible coordination of POMs to Cu(II) via oxo terminals as observed in the reported molecular copper complexes or copper oxide clusters stabilized by POMs [33–36] . Similarly, in FTIR, a notable red‐shift of [W=O] sym at 964 cm −1 to 949 cm −1 and significant broadening of the [W=O] asym band at 893 cm −1 after copper(II) exchange emphasize the coordination of POMs to Cu(II) (Figure S12) [32] .…”

“…The terminal metal‐oxo of the covalently attached POMs on the surface of Na x [POM]@TiO 2 can most likely act as sigma donor ligands to the copper ions as evident in the reported copper complexes of Keggin, Lindqvist, and Anderson POMs [33–35] . In the reported example, terminal oxo groups of hexaniobates were found to be coordinated to copper of a CuO nanocore containing 350 copper atoms [36] . By analogy, copper ions in Cu x [POM]@TiO 2 perhaps remained coordinated with POM without altering the core structure.…”

“…[49] Almost 56 cm À 1 band shifting of [W=O] t and 16 cm À 1 of [WÀ O-W] b due to copper exchange is implicating a possible coordination of POMs to Cu(II) via oxo terminals as observed in the reported molecular copper complexes or copper oxide clusters stabilized by POMs. [33][34][35][36] Similarly, in FTIR, a notable red-shift of [W=O] sym at 964 cm À 1 to 949 cm À 1 and significant broadening of the [W=O] asym band at 893 cm À 1 after copper(II) exchange emphasize the coordination of POMs to Cu(II) (Figure S12). [32] The TiÀ O stretching vibrations were observed as a broad band at 697 cm À 1 while the vibrations of Ti-OÀ Ti can be observed at 584 cm À 1 .…”

“…[33][34][35] In the reported example, terminal oxo groups of hexaniobates were found to be coordinated to copper of a CuO nanocore containing 350 copper atoms. [36] By analogy, copper ions in Cu x [POM]@TiO 2 perhaps remained coordinated with POM without altering the core structure. To confirm the unaltered core structure, Cu x [POM]@TiO 2 was first characterized by X-ray diffraction (XRD) studies.…”

Design and synthesis of novel polyoxometalate-based binary and ternary nanohybrids for energy conversion and storage

“…However, these molecular anions can range from 1 to 5 nm in size (Fig. 1) [22,23]. POMs show significant application potential for direct nanomaterial growth because of their diverse structures, charge densities, and reversible redox potentials [14,24,25].…”